Thin-layer batteries, for example, batteries with a LiPON electrolyte and a lithium-metal anode, are increasingly used in the electronics industry. The voltage across a battery of this type decreases along its operation to reach a critical voltage below which the battery is irreversibly damaged. Circuits using such batteries are thus generally equipped with a protection system stopping the battery discharge before it reaches this critical voltage. Such systems usually detect the moment when the battery voltage approaches its critical voltage to disconnect the battery from the load.
However, this critical voltage depends on the current pulled from the battery, which usually makes it necessary to size the protection system to the worst case, that is, to the highest critical voltage. Such a sizing adversely affects the performance and especially tends to disconnect the battery even when this is not necessary.
Further, the internal resistance of the battery varies according to temperature, which further complicates the problems, as will be discussed hereafter.
Such problems are particularly present in systems with an intermittent operation, for example, batteries powering self-contained sensors which periodically communicate data (regularly or not). In such systems, very short active periods alternate with inactive periods, which may be long.